In the modern era, organ transplantation has proven increasingly important as a solution to severe or end- stage diseases of the kidney, heart and liver, but unfortunately the results of lung transplantation have lagged considerably in terms of patient and graft survival rates. One of the main contributors to this poorer outcome is the development of primary graft dysfunction (PGD) within the first few days of lung transplantation. Dr. Jason Christie at UPenn has been studying the pathophysiology underlying PGD for the past decade, and has NIH- funded clinical studies underway in which blood samples are being collected pre- and post-lung transplantation in adults. An important new concept in immunology is that FOXP3+ T-regulatory (Treg) cells are key to normal regulation of immune responses, and that decreased Treg function likely contributes, clinically, to many forms of autoimmunity and inflammation. We hypothesize that pre-existing defects in Treg numbers or function, or defects in Treg numbers or function as a result of lung transplantation, may contribute to the development of PGD. We propose to test this hypothesis by assessing patients undergoing study in the underlying NIH-funded study of Dr. Christie that will last until 2014, using state-of-the art tests of Treg function that we have developed. Aim 1) of this ancillary study will assess aspects of Treg numbers and/or function pre-operatively and seek to ask whether any changes in Treg function are associated with increased rates or severity of PGD. Aim 2) of this ancillary study will asses whether the development of PGD in the very early post-Tx period is associated with decreased Treg numbers and/or function. Our studies will provide the first information on this clinically highly significant problem in lung Tx. Our findings, using samples obtained from 3 active lung transplant centers (Columbia, Indiana, Penn), may lead to new diagnostic or therapeutic interventions involving Treg cells therapies, or use of agents to enhance Treg function, in the very early post-operative period so as to overcome, or markedly decrease, the incidence and severity of PGD post-lung transplantation.